Gaskets for use in internal combustion engines are known. One known gasket design has multiple layers of steel and are referred to as "MLS" gaskets. In MLS gaskets, at least two sheets of steel are stacked together. Typically, there are three sheets with one middle sheet and two outer sheets. The outer surfaces have an elastomeric coating to accommodate imperfections that might interfere with creating a fluid tight sealing surface. In MLS gaskets, it is known to provide a bead to help establish suitable sealing stress levels and achieve a tight seal. However, one drawback to MLS gaskets is the increased expense of providing a very smooth surface finish to the clamping members. A second drawback is the cost of the elastomeric coating to compensate for imperfections on mating surfaces, such as cylinder heads or blocks.
Another known type of gasket design has outer facing layers made from graphite which are connected to outer cores. The facing layers and outer cores are attached to a central shim. Graphite outer facing layers conform to imperfections in mating surfaces and have a certain degree of resilience or springiness. U.S. Pat. Nos. 5,468,003 and 5,362,074, commonly assigned to Dana Corporation, describe gaskets of this type and each of their disclosures are incorporated herein by reference.
However, outer facing layers with graphite are susceptible to a relaxation phenomenon which results in a decrease in bolt tension and a corresponding reduction in sealing stress. The reduction of sealing stress could lead to an increased possibility of gasket leakage.